The present invention pertains generally to automated spray or coating systems such as powder or liquid coating systems and, more particularly, to control systems for controlling spray guns in automated coating systems.
In automated coating systems, for example of the type having one or more controlled material application spray guns (such as powder spray guns) positioned adjacent to a conveyor which carries parts to be coated past the guns, the guns are controlled (turned on and off and in some cases moved relative to the parts) to apply an optimal spray pattern to parts. Whenever there is a gap between parts on the conveyor, the guns should be turned off to stop spraying in order to minimize waste of material such as powder coating material. The turning on and off of the guns is referred to as xe2x80x9cgun triggeringxe2x80x9d. Automatic gun triggering gives the ability to optimize material usage. Automatic gun triggering uses a set of adjustable parameters which allow each gun of an array to automatically and efficiently apply a coating material to the parts. The automatic gun triggering parameters specify when and for how long each gun will spray a specific part.
In prior art systems of this type, the setting of optimal gun triggering parameters is difficult. An initial activation of the gun or guns has conventionally been accomplished by use of a photoeye detector which xe2x80x9cseesxe2x80x9d a part as it passes by on the conveyor. The first spray gun of an array is located at a fixed point from the photoeye. Many variables must be accounted for in achieving optimum spray coating, such as part size and shape, rate of conveyance, and spacing between parts. In a straight, uncalibrated automatic spraying set-up, the guns are turned on precisely at the front edge of a part, and turned off precisely at the back edge. This type of gun control may not completely coat the front and back edges of the part. Therefore, the triggering of the gun may have to be controlled to turn on prior to arrival of the part, and to continue spraying after the part has passed for complete coating of the part. This is called an xe2x80x9cextended wrapxe2x80x9d pattern which starts spraying prior to arrival of the leading edge of a part, and continues spraying after the part has passed. The gun on and gun off signals must be separately determined for extended wrap patterns. For example, if the guns were set to turn on before arrival of a part, this could cause the guns to turn off prior to arrival of the trailing edge of the part at the gun. A xe2x80x9cdelay offxe2x80x9d control is used for keeping the guns spraying until the trailing edge of the part has passed. In other gun triggering set-ups, it is desired to start spraying after the leading edge of the part has passed the gun. This is referred to as xe2x80x9crestricted wrapxe2x80x9d pattern. In this case, a xe2x80x9cdelay-onxe2x80x9d control is required to prevent the gun from spraying at the leading edge of the part. In this case also, the total spray duration must be adjusted to account for the delay-on control.
Prior art systems therefore have required setting of three different gun triggering control parameters: Delay-off (for extended wrap), Delay-on (for restricted wrap), and a parameter known as the xe2x80x9cPickoffxe2x80x9d. The Pickoff is the parameter which determines when the gun will start spraying relative to the position of a part approaching the gun. The distance xe2x80x9cDxe2x80x9d is the distance from the photoeye to the gun. If the Pickoff is set to equal the distance xe2x80x9cDxe2x80x9d then the gun will start spraying exactly when the part reaches the gun (i.e., when a leading edge of the part is aligned with the gun). The gun will start spraying at the Pickoff point, and spray for the length of the part, i.e., for the amount of time it takes the part to pass the gun G. The length of the part is automatically detected as the part is carried through the photoeye on the conveyor and this information is input to the controller. If the Pickoff is set at less than the fixed distance D, and no adjustments are made, the gun would start spraying before the forward edge of the part passes the gun, spray for the length of the part and stop spraying before the part has passed the gun. If the Pickoff is set at greater than the distance xe2x80x9cDxe2x80x9d, the gun will start spraying after the part reaches the gun, spray for the length of the part, and stop spraying after the rear edge of the part has passed the gun.
In the prior art, as schematically shown in FIG. 1, in order to spray a distance xe2x80x9cXxe2x80x9d before the part reaches the gun, and to continue spraying after the part has passed the gun for a distance xe2x80x9cYxe2x80x9d, the following setup is required:
Pickoff=Dxe2x88x92X
Delay-on=0 (since this is an extended wrap pattern and Delay-on is only used for restricted wrap patterns)
Delay-off=X+Y
The Pickoff, the part position at which the gun will start spraying, (Dxe2x88x92X) is less than the distance xe2x80x9cDxe2x80x9d. The gun will start spraying the distance xe2x80x9cXxe2x80x9d before the leading edge le of the part reaches the gun. Spray continues for the distance X plus the length xe2x80x9cPxe2x80x9d of the part plus the distance Y after the trailing edge of the part passes the gun. Thus, the Delay-off is set at X+Y meaning the controller holds the guns open for the distance of X+Y conveyor movement in addition to the distance P which is the length of the part. To achieve this spray pattern, a Dxe2x88x92X Pickoff value and X+Y Delay-off value are input to the controller.
One difficulty of this prior art gun triggering procedure lies in the fact that both the Pickoff and the Delay-off are functions of the same variable X. If there is a change in the distance xe2x80x9cXxe2x80x9d, the distance in front of the part that the gun begins spraying, both the Pickoff and the Delay-off parameters must be adjusted and input again into the controller. The Pickoff and the Delay-off parameters are not independent.
A numerical example of a prior art spray pattern is also shown in FIG. 1. In a case where the system is to apply a coating to part P such as a flat panel which is 20 inches long, in order to coat the leading and trailing edges of the panel it is desired to start spraying 6 inches (of conveyor travel) before the leading edge le of the part P arrives at gun G, and to continue spraying for 4 inches (of conveyor travel) after the trailing edge te of the part passes gun G. This xe2x80x9cextended wrapxe2x80x9d spray pattern covers a total distance of 30 inches (6xe2x80x3+20xe2x80x3+4xe2x80x3). In other words, 30 inches of the conveyor on which the part is mounted passes the gun G during the spray period.
If the gun is set to start spraying 6xe2x80x3 before the leading edge of the part reaches the gun G, the pickoff must be adjusted by subtracting 6xe2x80x3 from the 100xe2x80x3 distance D between the photoeye PE and gun G. Therefore, an xe2x80x9cadjusted pickoffxe2x80x9d of 96xe2x80x3 (Dxe2x88x92X) is input to the controller. To continue spraying for 4xe2x80x3 after the part passes the gun, the xe2x80x9cDelay-offxe2x80x9d of 10xe2x80x3 (6xe2x80x3+4xe2x80x3) is also input to the controller The length of the part P=20xe2x80x3 is read by the photoeye as the part passes the photoeye and also input to the controller. When the leading edge of the part P is 6xe2x80x3 from the gun, the gun will spray for 30xe2x80x3 of conveyor travel (6xe2x80x3+20xe2x80x3+4xe2x80x3). The gun will stop spraying 4xe2x80x3 after the trailing edge te of the part P passes the gun G.
If a change in the setup is made to spray, for example, 9xe2x80x3 before the leading edge, and still 4xe2x80x3 after the trailing edge, the length of spray before the leading edge must be changed, from 6xe2x80x3 to 9xe2x80x3. The Pickoff is set to start spraying 9xe2x80x3 before the leading edge le of the part reaches the gun G. Therefore, 100xe2x80x3xe2x88x929xe2x80x3=91xe2x80x3 is now input to the controller as the Pickoff. The Delay-off value must also be adjusted to 9xe2x80x3+3xe2x80x3=12xe2x80x3 and input into the controller. The part length of 20xe2x80x3 is unchanged. With these new parameters, the gun will start spraying 9xe2x80x3 before the leading edge of the part arrives at the gun and will spray continuously for 9xe2x80x3+20xe2x80x3+4xe2x80x3=33xe2x80x3 of conveyor travel. Thus, to generate this new triggering pattern, the Pickoff must be adjusted and reinput as well as the Delay-off. This makes this triggering system difficult and time consuming to configure and re-configure especially for different types of parts combined on a single conveyor.
Another problem associated with automated spray systems of the prior art is the inability of the operator to watch the spraying operation to confirm proper coating coverage. This is because a stationary control panel is typically located adjacent to a spray booth wherein the spray guns are located. Ideally, an operator is able to observe parts as they pass through the booth past the guns to assess the pattern and extent of coating coverage. However, since the operator must remain at the control panel, in some installations it is difficult to see from the panel location the parts as they are coated. This makes it more difficult to properly set the spraying parameters.
The present invention overcomes these and other disadvantages and shortcomings of prior art systems. The invention provides an automated coating application system and method in which the spraying parameters for different spray patterns are independently adjusted by the user in order to rapidly and accurately configure the system for optimum coating of a succession of conveyed parts. The automatic gun triggering system of the invention has an automatic gun triggering set-up feature which allows the operator to easily and rapidly set the triggering of the spray guns, by directly observing the movement of parts past the spray guns. The gun triggering settings or parameters are input to a control system through a hand-held mobile pendant having START SPRAY, STOP SPRAY, SAVE and SET PICKOFF input controls.
The invention uses three independent spraying parameters: Pickoff, Front-Edge-Spray and Back-Edge Spray.
In the invention, the Pickoff is always a fixed distance xe2x80x9cDxe2x80x9d from the photoeye to the gun. Because the photoeye and gun locations are fixed, the Pickoff does not change. The Pickoff is set only once unless the gun or/and the photoeye are physically moved. For this reason, it is referred to as the xe2x80x9cPermanent Pickoffxe2x80x9d.
The Front-Edge-Spray, if greater than zero, is the position of the front edge fe of the part before arriving at the gun, at which the gun starts spraying. If less than zero, the Front-Edge-Spray is the distance of travel of the front edge fe of the part past the gun, for which spray is withheld. If the Front-Edge-Spray is equal to zero, spray will start when the front edge fe is aligned with the gun.
The Back-Edge-Spray is the gun triggering parameter which determines when the gun will stop spraying relative to a position of the back edge of a part. If the Back-Edge-Spray is set at less than zero, the gun will stop spraying before the back edge of the part reaches the gun. If the Back-Edge-Spray is set at greater than zero, the gun will continue to spray after the back edge be of the part has passed the gun. If the Back-Edge-Spray is set at zero, the spray will stop when the back edge be is aligned with the gun.
In one example of the invention, described with reference to FIG. 2, in order to spray a distance xe2x80x9cXxe2x80x9d before the part reaches the gun (i.e., a xe2x80x9cFront Edge Sprayxe2x80x9d or xe2x80x9cFESxe2x80x9d), plus spray for the length P of the part, plus spray a distance Y after the part passed the gun (i.e., a xe2x80x9cBack-Edge-Sprayxe2x80x9d or xe2x80x9cBESxe2x80x9d), the following setup is required:
Pickoff=D
Front-Edge-Spray=X
Back-Edge-Spray=Y
The pickoff=D is fixed (xe2x80x9cPermanent Pickoffxe2x80x9d). The gun will start spraying at the distance xe2x80x9cXxe2x80x9d before the front edge fe of the part is aligned with the gun, spray for the length of the part P (as detected by a photoeye sensor), and spray a distance Y after the back edge be of the part P passes the gun. The Front-Edge-Spray distance xe2x80x9cXxe2x80x9d, and the Back-Edge-Spray distance xe2x80x9cYxe2x80x9d, are set independent of each other, so that adjustment of one does not require a corresponding adjustment of the other. Stated in another way, because the Front-Edge-Spray X is not determined by an adjustment of the Pickoff, a change in the Front-Edge-Spray does not require a corresponding adjustment of the Back-Edge-Spray, as is required in prior art systems.
In accordance with one aspect of the invention, there is provided a system for automatically applying a coating such as a powder coating to a succession of parts, and an automated control system for controlling triggering of one or more spray guns for optimized coating of each part. The gun triggering control system has three control parameters, START SPRAY, STOP SPRAY, and SET PICKOFF for triggering the spray guns on and off relative to the operator observed passage of a part past the spray guns. The triggering control parameters, preferably input through a hand-held pendant, are stored in a programmable controller which controls the operation of the spray guns. Once the triggering parameters are set by operator inputs from the hand-held pendant, the system is ready to commence automatic spray coating of a series of parts carried by the conveyor. Multiple gun triggering control parameters can be entered into the system for parts of differing dimensions. A part identification sensor identifies parts prior to arrival at the spray guns and triggers the spray guns according to the parameters stored for the identified part.
In accordance with another aspect of the invention, there is provided an automated coating application system having one or more spray guns operative to spray a coating onto parts carried by a conveyor past the spray guns. A sensor such as a photoeye is operative to detect the presence and length of a part carried by the conveyor past the sensor. A spray gun control system has input controls which control triggering of the spray guns. The input controls are connected to a programmable controller operative to trigger the spray guns to on and off states corresponding to Front Edge Spray and Back Edge Spray gun control parameters input by an operator through the input controls. The parts conveyed past the guns are coated according to the Front Edge Spray and Back Edge Spray gun control parameters. A change in either the Front Edge Spray or Back Edge Spray triggering parameters does not require a corresponding change in the other.
In accordance with another aspect of the invention, there is provided a method of triggering one or more spray guns in an automatic spray coating system having at least one spray gun located proximate to a conveyor. Parts to be coated are conveyed past the spray gun by a conveyor. The spray gun is operatively connected to a coating supply, and to a spray gun triggering control system operative to turn the spray guns on and off according to gun triggering control parameters input by an operator to the control system. The system has a sensor for sensing the presence and length of a part conveyed by the conveyor, and a control input device having START SPRAY, STOP SPRAY, SAVE and SET PICKOFF input controls. The method includes the steps of: observing a part as it is conveyed by the conveyor up to and past at least one of the spray guns of the system; selectively triggering one of the spray guns to an xe2x80x9conxe2x80x9d state by operation of the START SPRAY control of the control input device at a desired position of a front edge of the part relative to the spray gun to define a Front Edge Spray gun triggering control parameter; pressing the SET PICKOFF control when a front edge of the part is aligned with one of the spray guns, selectively triggering the spray gun to an off state by operation of the STOP control of the control input device at a desired position of a back edge of the part relative to the spray gun to define a Back Edge Spray gun triggering control parameter; storing the selected gun triggering parameters as a control recipe in the gun triggering control system by operation of the SAVE control; whereby a gun triggering control recipe is set for spraying the part conveyed by the conveyor according to the control recipe; and repeating this method for other parts input into the control system with other control recipes.
In accordance with another aspect of the invention, for automated spray coating arrangements which utilize a conveyor to convey parts past one or more spray guns for painting or coating, there is provided an automated method and system for determining spray gun triggering parameters based upon operator inputs according to observation of parts as they are conveyed past the guns. A sensor located proximate to a part conveyor senses the presence of a part, and records the front and back edges and length of the part in terms of encoder counts of conveyor movement. An operator presses a SET PICKOFF input control when the front edge of the part is aligned with the spray gun to provide a signal to the control system which indicates the distance from the sensor to the gun, referred to as a Permanent Pickoff. A START SPRAY input control is pressed when spraying is to commence, relative to a position of a part to the spray gun. A STOP SPRAY input control is pressed when spraying is to stop, relative to a position of the part to the spray gun. By the conveyor encoder counts, the system determines a Front Edge Spray gun triggering control by subtracting the START SPRAY encoder value from the Permanent Pickoff. The system determines a Back Edge Spray gun triggering control by subtracting from the STOP SPRAY encoder count the length of the part and the Permanent Pickoff. By this method and system, the Front Edge Spray and Back Edge Spray gun triggering control parameters can be independently set and adjusted by observation by an operator, to provide an easy way of achieving any desired spray pattern.
These and other aspects of the invention are herein described in particular detail with reference to the accompanying Figures.